1. Field of the Invention
This invention relates to a method of and an apparatus for cooling edge portions, e.g. peripheral and marginal edge portions, of one or more sheets, e.g. one or more glass sheets, to strengthen the edge portions of the sheets, and in particular, to method of and apparatus for extracting heat at a faster rate from edge portions of heated glass sheets supported on a bending iron than the central portions of the sheets to rapidly cool and strengthen the edge portions of the sheets.
2. Discussion of Technical Background
The method of laminating glass windows for vehicles, e.g. automotive windshields, usually includes the steps of forming the glass sheets, e.g. by placing a pair of glass sheets onto a mold commonly referred to as one of the following: a bending iron, a bending mold, a shaping mold and an outline mold, and moving the outline mold and glass sheets supported thereon through a heating furnace for gradual heating and gravity sagging of the pair of glass sheets to provide glass sheets having a desired shape. After the sheets are shaped, the sheets are slowly cooled during an annealing cycle to remove most of the stress from the glass sheets. Edge compression for such glass sheets is normally about 1500 to 2500 pounds per square inch (“psi”) (10.3 to 17.3×106 Pascals (“Pa”)). After the shaping and annealing operations, a sheet of polyvinyl butyral is placed between the glass sheets to provide a subassembly which is exposed to heat and pressure during a conventional laminating process to form a laminated glass window, e.g. a laminated automotive windshield.
It is generally understood that edge compression of less than about 1500 psi (10.3×106 Pa) increases the probability of damaging the edges of a laminated glass window, e.g. a laminated windshield during installation into a vehicle window opening. As can be appreciated, increasing the edge compression to at least 3000 psi, e.g. 3,000-5,000 psi (20.7-34.5×106 Pa) reduces the tendency of edge damage, e.g. during installation of the windshield.
U.S. Pat. No. (“USPN”) 5,938,810 discusses press-bending sheets utilizing forced area cooling. In general, a sheet of glass is heated to a formable state and pressed between a rigid mold and pressing member. The pressing member presses the heated sheet against the rigid mold to bend and cool the sheet. U.S. Pat. No. 5,938,810 recognizes that in some applications, for instance in windshields, it is desirable to cool the edge of the glass sheet at a faster rate than the central portion of the sheet to provide an enhanced edge temper on the glass sheet. The cooling of the glass edges is accomplished by using an internal air manifold that directs air to the edge of a heated glass sheet while the sheet is between the rigid mold and the pressing member.
U.S. Pat. Nos. 4,749,399; 5,679,124 and 6,015,619 also discuss techniques of cooling marginal edge portions of glass sheets supported on cooling rings to strengthen the edges of glass sheets.
Although there are techniques to cool the edges of a glass sheet while the sheet is between pressing molds, and to cool the marginal edges of a glass sheet while on a cooling ring; there are no satisfactory techniques to cool the peripheral edges of a pair of shaped glass sheets while supported on an outline mold, e.g. but not limited to outline molds, and/or shaping techniques, of the types discussed in U.S. Pat. Nos. 3,976,462; 4,375,978; 4,687,501; 4,894,080; 4,979,977 and 5,049,178.
As can be appreciated, it would be advantageous to provide a method of and apparatus for extracting heat at a faster rate from the peripheral and marginal edge portions of heated glass sheets supported on an outline mold than the central portions of the sheets to cool and strengthen at least the peripheral edge portions of the glass sheets.